Things due *by* a date, not *on* the date.

I have a basic question about the GTD system that I hope someone here can clarify: how do I classify something that needs to be done by a specific date, but not done on the day?

For example, if I'm a student and I have an assignment due in one month's time, do I put that assignment on the calendar? If so, how do I remember to work on it when I'm reviewing my next action lists? If I throw it in with the next actions, how do I keep track of when it's due? Putting it on both lists is a redundancy I would rather avoid.